TOKYO -- Two Russian fighter jets briefly entered Japan's airspace near the northern island of Hokkaido on Thursday, prompting Japan to scramble combat fighters and lodge a protest, Japan's Foreign Ministry said.

It was the first such intrusion in five years, a ministry official said. Former Japanese Prime Minister Yoshiro Mori is expected to visit Moscow later this month to discuss territorial matters.

Thursday was Japan's "Northern Territories Day", when rallies are traditionally held calling for the return of disputed islands off Hokkaido.

Russian Prime Minister Dmitry Medvedev landed on the remote island chain in July, prompting protests from Tokyo.

Medvedev's trip to the disputed islands in Russia's Far East -- known as the Southern Kuriles in Russia but as the Northern Territories in Japan -- prompted Japan's Ministry of Foreign Affairs to complain.

Unlike Japan's dispute with China over islands in the East China Sea, which are near potentially vast maritime oil and gas reserves, the feud with Russia has more to do with the legacy of World War Two.

Soviet soldiers seized the islands at the end of the war and the territorial row has weighed on diplomatic relations ever since, precluding a formal peace treaty.

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